Extending the π‐Skeleton of Multi‐Resonance TADF Materials towards High‐Efficiency Narrowband Deep‐Blue Emission

Multi-resonance TADF (MR-TADF) emitters are promising for high-resolution OLEDs, but the concurrent optimization of excited-state dynamics and color purity remains a tough challenge. Herein, three deep-blue MR-TADF compounds (BN1-BN3) featuring gradually enlarged ring-fused structures and increased rigidity are accessed by lithium-free borylation in high yields from the same precursor, with all the emitters possessing CIEy coordinates below 0.08. Structure-property investigations demonstrate a strategic improvement of the oscillator strength (fosc ) and acceleration of the reverse intersystem crossing (RISC) process by extending the π-skeleton, where BN3 realizes a maximum external quantum efficiency (EQE) of 37.6 % and reduced roll-off, thus showing the best efficiency reported for deep-blue TADF OLEDs. The internal regulation of the efficiency and color purity of these compounds validate the general effectiveness to achieve advanced deep-blue narrowband emitters with higher-order boron/nitrogen-based MR motifs.